The formation of mature germ cells in the adult male animal is a unique developmental system. Spermatogenesis requires the maintenance of a stem cell pool which can self renew and can undergo a complicated differentiation process to form the haploid male gamete. The introduction of new genes into mice provides a powerful method by which to study this complicated process and may reveal novel mechanisms for gene regulation. We propose studies in four areas. 1. To identify the cis-acting regulatory elements required for spermatid specific transcription of the mouse protamine-1 gene, which codes for a unique protein involved in sperm chromatin condensation. 2. To determine the role of RNA sequences in the translational regulation and stability of protamine message. 3. To establish the degree of macromolecular movement between syncytial spermatids during differentiation. 4. To analyze two transgenic mouse lines which process distinct characteristic defects in male germ cell development. These experiments represent a new approach to the study of spermatogenesis and will provide insight into the process of differentiation and gene regulation.